The New York Times
By AMY HARMON
Published: January 22, 2006
THERE are a lot of things I may never know about K2a2a, one of four founding mothers of a large chunk of today's Ashkenazi Jewish population and the one from whom - I learned last week - I am directly descended.
I may never know whether she lived 1,000 years ago or 3,000. I may never know if she was born in the Judea, as the scientists who identified her through mitochondrial DNA say they suspect. I will certainly never know her name.
I do know that I carry her distinctive genetic signature. My mother carried it, my mother's mother carried it, my daughter now carries it, too.
And the thrill of that knowledge - for the price of the $100 cheek swab test of my own DNA - may be all I can handle.
The popular embrace of DNA genealogy speaks to the rising power of genetics to shape our sense of self. By conjuring a biologically based history, the tests forge a visceral connection to our ancestors that seems to allow us to transcend our own lives.
But will our genetic identity undermine our cultural identity? The tests can add depth to what we have long believed, but they can also challenge our conception of who we are. The trauma some experience when their tests conflict with what they have always believed to be true has prompted some researchers to call for counseling to accompany the results.
Because the Y chromosome, which determines maleness, is passed unchanged from father to son, scientists can use it to determine whether two men share a common ancestor. When rare mutations do occur, they are unique to a single man and his male descendants, and scientists can often pinpoint when and where this founding father lived.
Mitochondrial DNA, which is passed on largely intact from mothers to their children, can be used similarly to trace maternal ancestry.
But each test can trace only one lineage back to a single ancestor. K2a2a was my mother's mother's mother's ... mother, for instance, and my father has taken the test so we can learn about his father's father's father's ... father.
But these kinds of tests can't teach me anything about any of the thousands of other ancestors of mine who were living 1,000 or 2,000 years ago.
A different kind of test, which promises to parse the percentage of a customer's genome that came from different geographical regions, can be misled by the reproductive shuffling of each generation.
Some anthropologists worry that what they call the "geneticization of identity" could lead to a dangerous view of race and ethnicity as biologically based. But many who have taken the tests say that the details of their DNA can underscore that we are all genetic cousins.
Why the genetic claiming of an ancient grandmother holds such emotional sway I am not quite sure. I mean, I've never even been to Ellis Island. And I have spent too many Christmases ordering in Chinese for it to come as a surprise that I am more likely to share mitochondrial DNA with Ashkenazi Jews than other groups.
But to judge by the growing throngs of other newly minted DNA genealogists, I'm not the only one to find appeal in the idea that the key to our past is lodged in our own genes.
On the "DNA-Genealogy" e-mail group last week, the buzz about the Jewish founding mothers was quickly supplanted by the news that scientists had traced a widely distributed genetic signature among people of Irish descent to a legendary Irish king.
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